(Not Applicable)
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The present invention relates to radiating systems and, more particularly, to improved radiation synthesizer systems enabling efficient use of small high-Q antennas by active control of energy transfer back and forth between an antenna reactance and a storage reactance.
The theory and implementation of Synthesizer Radiating Systems and Methods re described in U.S. Pat. No. 5,402,133 of that title as issued to the present inventor on Mar. 28, 1995. Further aspects are described in U.S. Pat. No. 6,229,494, titled Radiation Synthesizer Systems and Methods, as issued to the present inventor on May 8, 2001. These patents (xe2x80x9cthe""133 patentxe2x80x9d and xe2x80x9cthe ""494 patentxe2x80x9d) are hereby incorporated by reference.
A basic radiation synthesizer circuit, as described in the ""133 patent, which combines transfer circuits in both directions using two switches is shown in FIG. 1a. This circuit functions as an active loop antenna where the loop antenna L is the high Q inductive load and a capacitor C is used as the storage reactor. The FIG. 1a circuit uses two RF type switching transistors, shown as switches RC and DC, for rate and direction control, respectively. Because the devices are operated in a switch mode, efficient operation is obtained since, in theory, no instantaneous power is ever dissipated by such devices. A slower switching device, shown as power control switch PC, can be used to add energy to the circuit from the power supply as energy is radiated. The voltage and current sensor terminals VS and CS, respectively, are used to monitor and calculate the total amount of stored energy at any instant in time, while a feedback control circuit is used to maintain the total energy at a preset value through use of the power control switch PC.
In the FIG. 1a circuit, when the direction control switch is open, energy can be transferred from current through the inductor L to voltage across the capacitor C, as illustrated by the L to C energy transfer diagram of FIG. 1b. With the rate control switch closed, current flows from ground, through diode D1 and L, and back to ground through the rate control switch RC. In the absence of circuit losses, the current would continue to low indefinitely. When the rate control switch RC is opened, the inductor current, which must remain continuous, flows through diode D2 and charges up the capacitor C. The rate at which C charges up is determined by the switch open duty cycle of the switch RC. The capacitor will charge up at the maximum rate when the switch is continuously open. The charging time constant is directly proportional to the switch open duty cycle of the rate control switch RC.
When the direction control switch DC of FIG. 1a is closed, energy can be transferred from voltage across the capacitor to current through the inductor, as shown in the C to L energy transfer diagram of FIG. 1c. Diode DI is always back biased and is, therefore, out of the circuit. When the rate control switch RC is closed, the capacitor C will discharge through L, gradually building up the current through L. If the rate control switch is opened, the capacitor will maintain its voltage while the inductor current flows in a loop through diode D2. In this C to L direction transfer mode, the rate is controlled by the switch closure duty cycle of switch RC. The maximum rate of energy transfer occurs when the switch RC is continuously closed. Its operation is the inverse of that in the other direction transfer mode (L to C).
It should be noted that, in either direction, charge or discharge is exponential. Therefore, the rate of voltage or current rise is not constant for a given rate control duty cycle. In order to maintain a constant rate of charging (ramp in voltage or current), it is necessary to appropriately modulate the duty cycle as charging progresses. Duty cycle determinations and other aspects of operation and control of radiation synthesizer systems are discussed at length in the ""133 patent (in which FIGS. 1a, 1b and 1c referred to above appear as FIGS. 8a, 8b and 8c ).
In theory, since the power which is not radiated is transferred back and forth rather than being dissipated, lossless operation is possible. However, as recognized in the ""133 patent losses are relevant in high frequency switching operations, particularly as a result of the practical presence of ON resistance of switch devices and inherent capacitance associated with switch control terminals. While such device properties are associated with very small losses of stored energy each time a switch is closed, aggregate losses can become significant as high switching frequencies are employed. In addition, if small loop antennas are to be employed, for example, antenna impedance may be higher than basic switching circuit impedance levels, necessitating use of impedance matching circuits which may have less than optimum operating characteristics.
The basic radiation synthesizer circuit discussed above can be reduced to the simplified ideal model shown in FIG. 2. This model replaces the diodes in the basic circuit by ideal switches, and provides push-pull operation (current can flow in either direction through the loop antenna). The push-pull, or bipolar circuit, is more efficient than the single-ended circuit by a factor of 2 (3 dB). The FIG. 2 system includes four power switch devices comprising a switching circuit pursuant to the invention, a complete implementation of which is shown in FIG. 3. The FIG. 2 system includes loop antenna 12, storage capacitor 14 and power switch devices 21, 22, 23 and24, which will also be referred to as switch devices S1, S2, S3 and S4, respectively. Three possible states exist: linear charging of inductor current, linear discharging, and constant current. It is possible to synthesize any waveforn using this circuit, with waveform fidelity dependent on sampling speed.
FIG. 2 shows a basic form of radiation synthesizer system with a single switching circuit connected to the two input terminals of a standard loop antenna. Each switch may consist of several individual devices either connected in series or parallel in order to realize optimized performance at the desired radiation power level. At some frequencies of operation additional practical constraints may require consideration. As a first consideration, the device parameters may necessitate very low antenna input terminal impedance in order to realize acceptable performance. That impedance may not be compatible with a single-turn loop of appropriate size. As a second consideration, a single-turn loop may be subject to an electrical resonance when the antenna is moderately small. This resonance occurs when the distance around the loop perimeter approaches one-half wavelength at an operating frequency.
Pursuant to the ""494 patent, a multi-segment loop configuration using distributed switching electronics provides a solution addressing these considerations. An embodiment in which the antenna has been broken into four loop segments and uses four switching circuits controlled by synchronous signals is described by way of example in that patent. The effective terminal impedance that is presented to each switching circuit is equal to 1/N times the total loop impedance where N is the number of loop segments. Hence, the optimum low-impedance antenna impedance level may be achieved by dividing the loop into the appropriate number of segments. The electrical resonance of this approach occurs when each segment length approaches one-half wavelength. Therefore, the resonance is increased in frequency by a factor of N over the non-segmented approach. it is possible, using this approach to obtain acceptable performance at any frequency by properly segmenting the loop.
FIG. 3 shows a synthesizer radiating system 60, as described in the ""494 patent, employing a multi-segment loop radiator in the form of a single-turn loop separated into four segments 61-64. In FIG. 3, the single switching circuit of FIG. 2 is replaced by four switching circuits (i.e., four xe2x80x9csub-circuitsxe2x80x9d) 10a, 10b, 10c, 10d, each of which is coupled to the ends of two successive ones of loop segments 61-64, as shown. Each of the sub-circuits 10a-d may be similar to switching circuit 10 of FIG. 2, except for the described coupling to loop segments 61-64 instead of to the ends of continuous loop 12 as in FIG. 2. The multi-segment loop radiator system 60 thus comprises a loop antenna element configured as a plurality of successive loop segments 61-64 and a like plurality of switching circuits 10a-d each coupled to a different pair of loop segments. Each switching circuit (i.e., sub-circuit) includes switch devices arranged for controlled activation as described above to transfer energy back and forth from the loop segments to which it is coupled to a portion of said storage capacitance (i.e., to one of capacitors 14a-d of FIG. 3).
Although any number of segments may be utilized pursuant to design considerations as discussed, in FIG. 3 the plurality of successive loop segments consists of four loop segments 61-64, which are employed with a like plurality of switching circuits consisting of four switching circuits 10a-d, each having a respective capacitor 14a-d coupled thereto. Thus, in FIG. 3, the basic storage capacitance comprises a plurality of capacitive devices, one coupled to each switching circuit.
In a particular implementation, the multi-segment loop radiator system as represented in FIG. 3 may be constructed as a flexible ribbon including loop segments and switching circuits physically arranged as a continuous flexible loop capable of being supported by a jacket or other article of clothing. Such an operable while wearing system may desirable include a portable receiver/transmitter and portable battery coupled to the switching circuits to comprise an individually transportable communication system. Such receiver/transmitter (e.g., as described with reference to FIG. 13 of the ""133 patent) may typically be provided in miniaturized form and coupled in parallel to each of the switching circuits 10a-d to enable simultaneous excitation of loop segments 61-64.
Continuing work with synthesizer radiating systems has indicated the desirability of further development and improvement, including arrangements relating to aspects of signal feeds and provision of DC power to portions of a synthesizer radiating system, particularly in multi-segment antenna configurations.
Objects of the invention are, therefore, to provide new and improved synthesizer radiating systems, particularly such as enable one or more of the following advantages and capabilities:
improved control signal feed configurations;
control signal feed via fiber optic cables;
use of optical signal paths not subject to induced currents via inductive coupling;
improved DC supply configurations;
use of antenna loop segments in dual capacity to couple DC voltages;
use of multiple conductor antenna loop segments to couple a plurality of DC voltages; and
avoidance of separate DC supply conductors subject to induced currents via inductive coupling.
In accordance with the invention, a synthesizer radiating system, wherein energy is transferred back and forth between an inductive antenna element and storage capacitance by controlled activation of switching circuits, utilizes a loop antenna element configured as a plurality of successive loop segments. A plurality of switch modules are each coupled to a different pair of loop segments and each switch module includes switch devices arranged for controlled activation to transfer energy back and forth between the storage capacitance and the loop segments coupled to the switch module. The system may incorporate a control signal feed including at least one optical signal path coupled to each switch module for control of activation of the switch devices. The system may also include a DC supply including a first DC coupling to a loop segment, DC couplings between successive loop segments, and DC couplings between loop segments and selected switch modules. The DC couplings are arranged to enable coupling of a DC voltage to the switch modules via the loop segments, while limiting coupling of non-DC signals.
The system may further include an optical modulator responsive to a feed signal (e.g., representative of a signal to be radiated) to provide control signals via the optical signal paths. A plurality of optical demodulators, each coupled between an optical signal path and one switch module, process control signals provided via the optical signal paths for use to control activation of the switch devices.
The system may incorporate loop segments which each include at least first and second parallel conductor portions which are DC-isolated from each other. For use with such multi-conductor loop segments, a DC supply may include (i) a first DC coupling to a first conductor portion, DC couplings between successive first conductor portions, and DC couplings between first conductor portions and selected switching circuits, and (ii) a second DC coupling to a second conductor portion, DC couplings between successive second conductor portions, and DC coupling between second conductor portions and selected switching circuits, with the DC couplings arranged to limit coupling of non-DC signals. With this construction, the DC couplings may be arranged to enable coupling of a plurality of DC voltages to each switching circuit, via the respective at least first and second parallel conductor portions, while limiting coupling of non-DC signals.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.